Abnormality detection system, abnormality detection method, abnormality detection program, and method for generating learned model

ABSTRACT

A method and system that efficiently selects sensors without requiring advanced expertise or extensive experience even in a case of new machines and unknown failures. An abnormality detection system includes a storage unit for storing a latent variable model and a joint probability model, an acquisition unit for acquiring sensor data that is output by a sensor, a measurement unit for measuring the probability of the sensor data acquired by the acquisition unit based on the latent variable model and the joint probability model stored by the storage unit, a determination unit for determining whether the sensor data is normal or abnormal based on the probability of the sensor data measured by the measurement unit, and a learning unit for learning the latent variable model and the joint probability model based on the sensor data output by the sensor.

TECHNICAL FIELD

Embodiments related to an abnormality detection system, an abnormalitydetection method, an abnormality detection program, and a method forgenerating a learned model.

BACKGROUND

Conventionally, identification of failure determination and failurecause of a machine has been carried out by comparing sensor data at thetime of normal operation of the machine with sensor data at the time offailure in the past (for example, see a flowchart showing processingroutine of failure determination of FIG. 13 of Patent Literature 1below). In this determination, in order to accurately and efficientlycompare sensor data, failure cause can be classified highly accuratelyand efficiently by accurately and efficiently selecting a sensor whichis a transmission source of the sensor data.

However, when the number of selected sensors is large, a huge number ofman-hours are required to select an appropriate sensor. In addition, inorder to select an appropriate sensor, it was necessary to haveknowledge of each sensor attached to the machine and knowledge ofmachine-like characteristics of a target machine.

Related background art citation: patent literature 1: JP 2012-098901 A

With regard to the technical problem being solved, machines withadvanced control today are controlled and managed by multiple sensors.For example, in automobiles, more than 100 types of sensors areinstalled per vehicle. In the case of new machines and unknown failures,even those with an advanced expertise and abundant experience could notdeal with such case. Therefore, it is desired to realize a method or asystem that efficiently selects a sensor without requiring advancedexpertise or abundant experience.

Furthermore, even if sensor selection can be made efficiently, adefinition of sensor data, including noise, error, and failure in eventsthat need to be addressed, is complicated. Besides, depending on anapplication to be applied, the definition of the event that needs to beaddressed is different, so general-purpose means to detect sensor's datais desired.

In order to detect sensor data, it is necessary to design an abnormalityscore function for each sensor data and each application. Therefore, itused to be necessary to design an abnormality score function each timesensor data and the number of application increased, and there used tobe a fear that information important for abnormality detection is missedin feature design.

In data and application sensor data frequency domain, if an event is arare event in the first place and multiple factors overlap, the model,rule, or threshold design was very difficult, so a more generalized andadaptive system is demanded.

In order to solve the problem in the above-described prior art,embodiments of the present invention provide, for example, anabnormality detection system, an abnormality detection method, anabnormality detection program, and a method for generating learnedmodel, which learns various sensor data and application data output froman information system supporting social infrastructure such as electricpower, water supply, gas, transportation, communication, medical care,finance, service, and determines (including predicting)normality/abnormality of possible events.

SUMMARY OF EMBODIMENTS

An abnormality detection system of the present invention includes:storage means for storing a latent variable model and a jointprobability model previously learned; acquisition means for acquiringinput data of abnormality detection target; an encoder for inferring alatent variable from the input data based on the latent variable modelstored in the storage means; a decoder for generating restored data fromthe latent variable based on the joint probability model stored in thestorage means; and determining means for determining whether the inputdata is normal or abnormal based on deviation between the input data andthe restored data.

In addition, in the abnormality detection system of the presentinvention, the determining means determines an amount of deviationbetween the input data and the restored data based on probabilitycalculated according to parameters obtained in processes at the encoderand decoder.

In addition, in the abnormality detection system of the presentinvention, the determining means calculates deviation of a component foreach dimension of the input data and the restored data and determinesabnormality when there is a large divergence in any dimension.

In addition, the abnormality detection system of the present inventionfurther includes learning means for learning the latent variable modeland the joint probability model based on training data composed ofnormal data.

In addition, in the abnormality detection system of the presentinvention, the measuring means constructs the encoder and the decoder byany one of VAE, AAE, LVAE, ADGM.

Embodiments of the present invention can be described not only as aninvention of abnormality detection system as described above, but alsoas an invention of abnormality detection method and abnormalitydetection program respectively as follows. They are substantially thesame invention except for being in different categories, and achieve thesame actions and effects. The present invention can also be described asan invention of method for generating a learned model used in theabnormality detection system, the abnormality detection method, and theabnormality detection program described above.

An abnormality detection method according to the present invention is anabnormality detection method executed by an abnormality detection systemincluding storage means for storing a latent variable model and a jointprobability model previously learned, the abnormality detection methodincluding: an acquisition step of acquiring input data of abnormalitydetection target; an inference step of inferring a latent variable fromthe input data based on the latent variable model stored in the storagemeans; a generation step of generating restored data from the latentvariable based on the joint probability model stored in the storagemeans; and a determination step of determining whether the input data isnormal or abnormal based on deviation between the input data andrestored data.

An abnormality detection program according to the present inventioncauses a computer to function as: storage means for storing a latentvariable model and a joint probability model previously learned;acquisition means for acquiring input data of abnormality detectiontarget; an encoder for inferring a latent variable from the input databased on the latent variable model stored in the storage means; adecoder for generating restored data from the latent variable based onthe joint probability model stored in the storage means; and determiningmeans for determining whether the input data is normal or abnormal basedon deviation between the input data and the restored data.

A generation method for generating a learned model according to thepresent invention is a generation method for generating a learned modelincluding a latent variable model and a joint probability model forperforming abnormality detection of input data, the generation methodincluding: a training data acquisition step of acquiring at least one ormore pieces of training data consisting of normal data; an inferencestep of inferring a latent variable from the training data based on thelatent variable model; a generation step of generating restored datafrom the latent variable based on the joint probability model; adeviation calculation step of calculating deviation between the trainingdata and the restored data; and a parameter updating step of updatingparameters of the latent variable model and the joint probability modelbased on the deviation.

With respect to advantageous effects, according to the presentinvention, it is possible to select a sensor that is considered to beeffective for classifying failure cause more easily than in the past.For example, it is possible to select a sensor that is considered to beeffective for classifying failure cause without requiring machineknowledge.

According to the present invention, it is possible to reduce falsealarms of abnormality determination by properly reflecting a state of adevice on abnormality determination. In addition, abnormalitydetermination at an earlier stage becomes possible according to thefluctuation factor of device operation data. By doing so, it is possibleto present appropriate response behavior to maintenance personnel andoperators.

According to the present invention, it is possible to suppress theinfluence of outliers by updating learning data using sensor data whichis diagnosed to be normal. Moreover, it is possible to followdeterioration over time.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated in drawing figures in which:

FIG. 1 is a functional block diagram of an abnormality detection systemaccording to an embodiment of the present invention.

FIG. 2 is a figure illustrating a hardware configuration of theabnormality detection system according to the embodiment of the presentinvention.

FIG. 3 is a flowchart showing a process (abnormality detection method)executed by the abnormality detection system according to the embodimentof the present invention.

FIG. 4 is a flowchart showing a process (abnormality detection method)executed in the embodiment of the abnormality detection system accordingto the embodiment of the present invention.

FIG. 5 shows an abnormality detection system according to the embodimentof the present invention using VAE (part 1).

FIG. 6 shows an abnormality detection system according to the embodimentof the present invention using VAE (part 2).

FIG. 7 is a flowchart showing a process (abnormality detection method)executed by the abnormality detection system according to the embodimentof the present invention using the VAE.

FIG. 8 is a conceptual diagram showing an abnormality detection systemaccording to a second embodiment of the present invention using AAE.

FIG. 9 is a conceptual diagram showing an abnormality detection systemaccording to a third embodiment of the present invention using LVAE.

FIG. 10 is a conceptual diagram showing an abnormality detection systemaccording to a fourth embodiment of the present invention using ADGM.

DETAILED DESCRIPTION

Hereinafter, preferable embodiments of an abnormality detection system,an abnormality detection method, and an abnormality detection programwill be described in detail together with the drawings. In thedescription of the drawings, the same reference numerals are given tothe same elements, and redundant explanations are omitted.

FIG. 1 is a functional block diagram of an abnormality detection system1 according to an embodiment of the present invention. As shown in FIG.1, the abnormality detection system 1 includes a storage unit 10(storage means), an acquisition unit 11 (acquisition means), ameasurement unit 12 (measurement means), a determination unit 13(determination means) and a learning unit 14 (learning means).

The storage unit 10 stores a latent variable model and a jointprobability model. The storage unit 10 is a data base, for example. Theacquisition unit 11 acquires the sensor data output by the sensor. Themeasurement unit 12 measures the probability of the sensor data acquiredby the acquisition unit 11 based on the latent variable model and thejoint probability model stored by the storage unit 10. The determinationunit 13 determines whether the sensor data is normal or abnormal basedon the probability of the sensor data measured by the measurement unit12. The learning unit 14 learns the latent variable model and the jointprobability model based on the sensor data output by the sensor.

The measurement unit 12 may convert the sensor data acquired by theacquisition unit 11 into a dimension lower than the dimension of thesensor data based on the latent variable model stored by the storageunit 10, and may convert it into the original dimension based on thejoint probability model stored by the storage unit 10, thereby measuringthe probability. The measurement unit 12 may measure the probabilityusing a variant self-coder. The learning unit 14 may learn the latentvariable model and the joint probability model based only on the sensordata output by the sensor at the normal time.

The abnormality detection system 1 is composed of hardware such as aCPU. FIG. 2 shows an example of hardware configuration of theabnormality detection system 1. As shown in FIG. 2, the abnormalitydetection system 1 shown in FIG. 1 is configured as a computer systemthat physically includes a CPU 100, a RAM 101 which is a main storagedevice, and a ROM 102, an input/output device 103 such as a display, acommunication module 104, and an auxiliary storage device 105, and thelike.

The function of each function block of abnormality detection system 1shown in FIG. 1 is realized by loading predetermined computer softwareon the hardware such as CPU 100 and RAM 101 shown in FIG. 2, causing theinput/output device 103, the communication module 104, and the auxiliarystorage device 105 to operate under the control of the CPU 100, andreading and writing data in the RAM 101.

Steps included in abnormality detection system 1: The abnormalitydetection system 1 includes three steps (FIG. 3).

step 1; step of simultaneously learning latent variable model and jointprobability model (realized by learning unit 14).

step 2; step of measuring the test data probability p(x) using thelatent variable model and the joint probability model learned (realizedby the acquisition unit 11 and the measurement unit 12).

step 3; step of determining whether it is normal or abnormality usingthe information on the probability p(x) (realized by the determinationunit 13).

[1. Step 1] Step 1 is a step of simultaneously learning the latentvariable model and the joint probability model.

In step 1, a conditional probability p(z|x) is learned from anobservation variable x to a latent variable z, and a conditionalprobability p(x|z) is learned from the latent variable to theobservation variable.

When learning the conditional probability p(z|x) and the conditionalprobability p(x|z), a neural network may be used. By using the neuralnetwork, it is possible to learn linearly with respect to the number ofparameters regardless of the observed number of pieces of data.

The latent variable model is obtained by modeling the conditionalprobability p(z|x) using a neural network, for example. The latentvariable model is stored by the storage unit 10.

The joint probability is expressed by p(x, z) or p(z)·p(x|z). The jointprobability model is obtained by modeling the joint probabilityindependently using, for example, a neural network. The jointprobability model is stored by the storage unit 10.

The neural network is not limited in its composition. For example, itmay include a total coupling layer, a nonlinear function (sigmoid,relu), a batch normalization layer, a dropout layer.

The input data (sensor data output by the sensor) is acquired from thesensor and the like by the acquisition unit 11. The input data is notparticularly limited. The input data is, for example, a multidimensionalarray, a tensor, or the like. The input data acquired by the acquisitionunit is not limited to sensor data from the sensor, but various data maybe the target as long as it is data to be subjected to abnormalitydetection.

When the input data x is an n-dimensional vector, each value is, forexample, a continuous value, a discrete value, or the like. When thereare multiple pieces of input data, it can be extended tomultidimensional array or tensor.

Specific examples of sensor include a camera mounted on the robot, athree-dimensional acceleration sensor, an actuator, a temperaturesensor, a humidity sensor, and the like. Specific examples of sensordata include image data from the camera, position, velocity, andacceleration information from the three-dimensional acceleration sensor,the current and voltage amount applied to the actuator, those separatedby a window width in an appropriate time, or one obtained byfrequency-decomposing each one of them.

In step 1 to step 3, SVM or LOF may be used to determine whether it isnormal or abnormal, or a variational auto encoder (hereinafter referredto as VAE) may be used to determine whether it is normal or abnormal.Especially, it is preferable to use VAE (FIGS. 5 to 7).

At this time, when learning the latent variable model, that is, theconditional probability p(z|x) from observation variable x to latentvariable z using VAE in step 1, the learner is called an encoder. On theother hand, when learning the conditional probability p(x|z) from thelatent variable z to the observation variable x, the learner is called adecoder.

The input of the encoder is sensor data, obtained by testing the device(sampling at an appropriate time interval is given for a fixed time). Itshould be noted that the test is performed a plurality of timescontinuously or periodically. The output of the decoder is representedby abnormality degree and probability of each dimension of sensor data.

The VAE can issue probability values more easily than SVM or LOF.Therefore, the abnormality detection system 1 makes it easier to compareabnormality scores when using VAE, even for sensors with differentphysical quantities than when using SVM or LOF.

In addition, the VAE can perform nonlinear conversion of data expressionmore easily than SVM or LOF. Therefore, the abnormality detection system1 can create a more complicated data expression distribution when usingVAE than when using SVM or LOF.

The VAE can also issue abnormality scores for each dimension of inputdata as compared with SVM or LOF. Therefore, in abnormality detectionsystem 1, it is easier to identify the input data source that becomesthe cause of an abnormality event when using VAE than when using SVM orLOF.

The VAE can learn similarity faster than SVM or LOF. Therefore, theabnormality detection system 1 does not need to manually designsimilarity between data when using VAE as compared with a case of usingSVM or LOF.

For example, when using VAE,

-   -   p(z)˜N(0, I)    -   p(x|z)˜N(μ(z), σ(z))    -   N(μ, σ) is a normal distribution consisting of mean μ and        variance σ.    -   μ(z), σ(z) are outputs from the neural network.

In the abnormality detection system 1, the loss function is minimizedwhen learning the conditional probability p(z|x) and p(x|z) in theencoder and decoder. For example, a negative logarithmic probability−log p(x) or the like can be used as the loss function:

−log p(x)=−log Πp(x_i)=−Σ log ∫p(x_i|z)p(z)dz

When integrating with z, the variational lower limit is calculated bythe following equation. For the variational lower limit, the positivelogarithmic probability log p(x)=log Πp(x_i) is evaluated from the lowerlimit.

−log Πp(x_i)=−Σ_i log ∫p(x_i|z;θ)p(z)dz

<=−Σ_iq(z|x;ξ)∫ log p(x_i|z;θ)p(z)/q(z|x_i;ξ)dz

=Σ_iE_{q(z|x_i;ξ)}[p(x_i|z;θ)]−KL(p(z)∥q(z|x_i;ξ))

Here, E_{q(z|x_i;ξ)}[·] is the expected value for q(z|x_i;ξ). KL(p∥q) isthe KL distance of the distribution p, q.

In order to maximize the above-mentioned variational lower limit, θ andξ are optimized. At this time, the learning speed can be increased bythe inverse error propagation method. For example, a ReparameterizationTrick can be used.

[2. Step 2]: Step 2 is a step of measuring the test data probabilityp(x) using the learned latent variable model and the joint probabilitymodel.

[3. Step 3]: Step 3 is a step of determining whether it is normal orabnormal using the information on the probability p(x).

In step 3, whether or not the test data probability p(x) is smaller thanthe threshold value, whether or not the nth-order differentiation of thetest data probability p(x) is smaller than the threshold value, or acombination thereof is used to determine whether it is normal orabnormal.

For example, when determining whether the value indicated by certainsensor data is normal or abnormal, conversion is made to x→z→x′, and atthat occasion, whether normal or abnormal can be determined by measuringthe difference between x′ and x.

For the sensor, its target and its number are not limited. For example,it may be strength per time, or strength per frequency. Alternatively,the sensor may be for different devices.

In a first embodiment, as described above, when disturbance probabilitydistribution changes during normal operation and during abnormality inrepetitive operation, the abnormality detection system 1 learnsprobabilistic model P with normal data, and predicts the observationdata x, probability p(x) change by P by abnormality.

Hereinafter, as an example of an embodiment of the present invention, asystem that executes five procedures is shown. Procedures 1 to 5 ofabnormality detection system 1 will be described below (FIG. 4).

[Procedure 1]: In procedure 1 (realized by the acquisition unit 11),preprocessing on the input data is performed. For example, spectrumconversion may be performed.

[Procedure 2]: In procedure 2 (realized by the learning unit 14), theprobabilistic model P is learned so as to input the data group in thenormal state as training data and restore the input data. For example, avector in which spectra are arranged can be input x.

When the number of dimensions is several thousand dimensions, it isdifficult to estimate the probability model of a high dimensionalvector. Therefore, in abnormality detection system 1, deep learning isused for estimation of probability model. For example, it becomes thefollowing latent variable model. Note: “:=” in the followingmathematical expression indicates the meaning of “to define”.

p(x;θ):=∫p(x,z;θ)dz p(x,z;θ):=p(x|z;θ)p(z)

In the above: z is generated from N(0, I), then from z, x is generatedfrom N(μ(z;θ), σ(z;θ)). However, the neural network characterized byμ(z;θ), σ(z;θ) parameter θ is used. Then, θ is optimized so as tomaximize the log probability Σ log p(x;θ) of the training data X.

The optimization of θ is difficult because of the calculation of the sumof the log probability.

p(x;θ):=∫p(x|z;θ)p(z)dz

Therefore, in abnormality detection system 1, the following variationallower limit is used.

$\begin{matrix}{{\log \; {p\left( {x;\theta} \right)}}:={\log {\int{{p\left( {x,{z;\theta}} \right)}{dz}}}}} \\{= {\log {\int{{p\left( {x,{z;\theta}} \right)}{q\left( {{zx};\phi} \right)}\text{/}{q\left( {{zx};\phi} \right)}{dz}}}}} \\{>={\int{{q\left( {{zx};\phi} \right)}\log \; {p\left( {x,{z;\theta}} \right)}\text{/}{q\left( {{zx};\phi} \right)}{dz}}}} \\{= {{{Eq}\left( {{zx};\phi} \right)}\left\lbrack {\log \; {p\left( {x,{z;\theta}} \right)}\text{/}{q\left( {{zx};\phi} \right)}} \right\rbrack}} \\{= {L\left( {\theta,\phi} \right)}}\end{matrix}\quad$

Here, φ is a parameter that characterizes a neural network thatgenerates a joint probability model. In the above equation: q(z, x)means the probability distribution defined by the neural network. Then,q(z|x) means the conditional probability of x conditioned by zcalculated with its probability distribution q(z, x).

At this time, in order to maximize L(θ, φ), θ and φ are simultaneouslyoptimized by using a variational auto encoder (hereinafter referred toas VAE).

L(θ,φ)=Eq(z|x;φ)[log p(x,z;θ)/q(z|x;φ)]

Specifically, the gradients dL/dθ and dL/dφ are obtained for the L(θ, φ)maximization parameters θ and φ by utilizing the stochastic gradientdescent method, and θ and φ are simultaneously optimized.

When estimating the gradient dL/dφ by the Monte Carlo method, thevariance can be large. Therefore, by using a variable conversion trick(also called a reparameterization trick), the gradient dL/dφ can beestimated faster.

For learning of q(z|x;φ) at the encoder and p(x|z;θ) at the decoder, aneural network is used.

[Procedure 3]: In procedure 3 (realized by the measurement unit 12)learned encoders and decoders are prepared, and probability p(x) by P iscalculated with determination data which performs abnormality detectionas an input. The probability p(x) is correlated with the abnormalitydegree of each dimension with respect to the output result of thelearned encoder and decoder with respect to the determination datainput.

[Procedure 4]: In procedure 4 (realized by measurement unit 12 ordetermination unit 13), probability p(x) is converted into score S(x) tobe smoothed. For example, conversion processing includes logarithm andthe like.

When the score S(x) value is bumpy, the smoothed version may be used asthe output. For example, Locally Weighted Scatterplot Smoothing can beused.

However, when the rise of change is delayed by the above smoothingmethod, it is possible to adopt a smoothing method in which the rise ofchange is earlier.

[Procedure 5]: In procedure 5 (realized by the determination unit 13),when S(x) exceeds the threshold value, it is determined as abnormality.

With respect to certain processing actions, the abnormality detectionsystem 1 learns the latent variable model and the joint probabilitymodel at the same time. Therefore, the abnormality detection system 1does not require feature design. A neural network may be used formodeling the latent variable model and the joint probability model.

The abnormality detection system 1 is characterized in that input datain a step that simultaneously performs learning of the latent variablemodel and joint probability model is a multidimensional array or atensor. Therefore, abnormality detection system 1 does not require priorknowledge about data and applications.

The abnormality detection system 1 consists of n sensors and learns njoint probability models. Therefore, according to the abnormalitydetection system 1, even if the number of sensors increases, theabnormality detection system 1 can deal with by learning a jointprobability model. Specifically, abnormality can be detected byconsidering the correlation between n sensors.

The abnormality detection system 1 uses a neural network when learningthe conditional probability p(z|x) and the conditional probabilityp(x|z). Therefore, according to abnormality detection system 1, learncan be performed linearly with respect to the number of parametersregardless of the number of sensor data observed.

According to the abnormality detection system 1, for example, sensordata transmitted from a large number of sensors provided in manymachines, for example, a high dimensional sensor data including imagedata, or sensor data including combinations thereof can be handledintegrally. Therefore, abnormality detection can be performed withhigher efficiency and higher processing speed.

The abnormality detection system 1 uses SVM, LOF, or VAE when learningthe latent variable model. Therefore, the abnormality detection system 1can nonlinearly convert input data expression. In particular, when usingVAE, nonlinear conversion can be performed regardless of the number ofparameters of input data.

When the abnormality detection system 1 uses VAE, the abnormalitydetection system 1 can learn similarity from sensor data. Therefore, theabnormality detection system 1 does not need to manually design thesimilarity design between sensor data.

When the abnormality detection system 1 uses VAE, the abnormalitydetection system 1 can acquire the characteristic which becomes thebasis of sensor data by dropping the dimension of sensor data.Therefore, the abnormality detection system 1 can convert a wider rangeof data expressions.

When the abnormality detection system 1 uses VAE, the abnormalitydetection system 1 can convert data expressions not only by the numberof parameters of data but also by linear calculation time. Therefore,the abnormality detection system 1 can perform conversion of dataexpressions with high efficiency.

In the abnormality detection system 1, devices in different places maybe configured by communicating using communication means. The sensordata is sent to another arithmetic unit by a communication means, andlearning and abnormality detection determination can be performed by thearithmetic unit.

For example, it is possible to perform a notification corresponding toan action determined by analyzing the determination result by theabnormality detection system 1 and an output processing to makepredetermined control.

Also, the abnormality detection system 1 does not limit the location ofeach step. For example, installation of sensor and implementation oflearning step can be performed in different places. The location ofabnormality detection or abnormality determination is not particularlylimited. The abnormality detection and the abnormality determination canbe done in the same place or in different places.

In a second embodiment, although the abnormality detection system 1according to the first embodiment has been mainly explained in the caseof using VAE as a model of machine learning, in this second embodiment,a case in which adversarial auto encoder (AAE) is used as a model ofmachine learning will be described as follows.

FIG. 8 is a conceptual diagram showing an abnormality detection systemaccording to a second embodiment of the present invention using AAE.When AAE is used for abnormality detection system, as shown in this FIG.8, it is a feature to learn discriminators in addition to learning ofencoder and decoder.

A flow of learning processing of AAE will be described. The learning ofthe AAE is performed in two stages of a restoration phase(Reconstruction phase) in which the encoder and the decoder are learnedand a regularization phase in which the discriminator is learned.Learning at the restoration stage firstly inputs the training data xwhich is normal data to the encoder, infers the expression z (latentvariable z) of the input data, inputs the expression z of the input datato the decoder, and generates the restored data x˜. The latent variablemodel is to infer the expression z of the input data. The jointprobability model is to generate the restored data x˜ from theexpression z. Next, the training data x is compared with the restoreddata x˜ to calculate a reconstruction error. Then, by referring to thereconstruction error, the parameters of the encoder and decoder areupdated, for example, by the stochastic gradient descent method so as toreduce the reconstruction loss.

In the learning at regularization stage, discriminators are learned, andat that time, learning is also performed for encoders that infer theexpression z₀ of input data to be input to the discriminator. First, thetraining data x which is normal data is input to the encoder, and theexpression z₀ of the input data is inferred based on the latent variablemodel, and on the other hand, sampling is performed from the samplegenerator (Sampler) to produce a false expression z₁. It is desirable toprepare multiple z₀ and z₁ for suitable learning. Based on z₀ and z₁,training data (z₀, 0), (z₁, 1) to be input to the discriminator arecreated. Here, 0 or 1 is a correct label. It indicates whether eachtraining data is an expression z₀ based on normal data or a falseexpression z₁. In the discriminator, learning is performed so as todiscriminate between expression z₀ based on normal data and falseexpression z₁ using the training data (z₀, 0), (z₁, 1). Specifically, inorder to distinguish the training data (z₀, 0) based on the normal datafrom the false training data (z₁, 1) sampled from the sample generator(Sampler), the discriminator first updates the parameter of thediscriminator. The discriminator then updates the parameters of theencoder to confuse the network for discrimination at the discriminator.The learned discriminator outputs the probability that the input is realdata (the probability that the input is a sample of the priordistribution). In this way, a regularization error is obtained in theprocess of distinguishing between normal data and false data in thediscriminator, and not only the discriminator but also the parameters ofthe encoder are updated and learned using the regularization error, sothat this improves the accuracy of inference in the encoder and improvesthe discrimination accuracy of the discriminator.

A flow of abnormality detection processing using AAE will be described.A learned model is prepared with sufficient learning. The data ofabnormality detection target is input into the encoder of the learnedmodel, the expression of the data of abnormality detection target isinferred, and the restored data is generated from the expression in thedecoder. The obtained restored data is compared with the input data ofabnormality detection target, and abnormality is detected from thedeviation between them. In addition, by inputting the expression ofabnormality detection target data to the discriminator, it is possibleto discriminate whether it is an expression based on normal data or afalse expression.

As described above, according to the abnormality detection system usingAAE, the latent variable model and the joint probability model arelearned based on normal data in advance. At the same time, with regardto the discriminator, learning is performed. By using thediscriminator's output, not only the discriminator but also the encoderand decoder are learned together. Therefore, highly accurate abnormalitydetection becomes possible. In AAE, complexity distribution can be usedif sampling is possible, and therefore it is expected that theexpressive power of the decoder is increased and the accuracy ofgeneration is increased.

In a third embodiment, the case of using LVAE (Ladder Variational AutoEncoder: Ladder Variable Self Coder) as a machine learning model will beexplained.

FIG. 9 is a conceptual diagram showing an abnormality detection systemaccording to the third embodiment of the present invention using LVAE.When LVAE is used for the abnormality detection system, as shown in FIG.9, learning of the encoder and the decoder is performed. There is afeature in that the parameters of the encoder are used while thisdecoder generates restored data from the expression z.

The flow of learning processing of LVAE will be described. In thelearning of LVAE, the training data x, which is normal data, is input tothe encoder, the expression z (latent variable z) of the input data isinferred, the expression z of the input data is input to the decoder,and the restored data x˜ are generated. This feature is the same as thefirst and second embodiments. In detail, as shown in FIG. 9, in thelatent variable model, the result for each hierarchy is obtained fromthe input data x through each hierarchy in the order of d₁→d₂→d₃, andfinally the expression z₃ is generated. In the joint probability model,the result for each hierarchy is obtained from the expression z₃ througheach hierarchy in the order of z₃→z₂→z₁, and finally the restored data xis generated. The number of hierarchies is an example, and it is notlimited thereto.

In the decoder, when generating restored data x˜ via the order ofz₃→z₂→z₁, the average μ^(˜) ₃ and variance σ^(˜) ₃ obtained from d₃ inthe encoder are used for sampling of z₃. By adding noise ε₃ at the timeof sampling of z₃, error back propagation is enabled even if there is astochastic function portion. Similarly, the average μ₂ and the varianceσ₂ obtained from d₂ in the encoder are used to find the average μ₂ andthe variance σ₂ for sampling of z₂. Similarly, the average μ^(˜) ₁ andthe variance σ^(˜) ₁ obtained from d₁ in the encoder are used to findthe average μ₁ and variance σ₁ for sampling of z₁. In this manner, ineach layer of the decoder, processing of the decoder is performed byusing parameters in the corresponding layer of the encoder. In thismanner, the restored data x˜ generated in the decoder is compared withthe training data x to calculate the difference, and the parameters ofeach layer of the encoder and decoder are updated so as to eliminate thedifference. After that, learning is repeated so that the training data xand restored data x˜ coincide with each other.

A flow of abnormality detection processing using LVAE will be explained.A learned model with sufficient learning is prepared. The data ofabnormality detection target is input into the encoder of the learnedmodel, the expression of the data of abnormality detection target isinferred, and the restored data is generated from the expression in thedecoder. The obtained restored data is compared with the input data forabnormality detection target, and abnormality is detected from thedeviation between them.

As described above, according to the abnormality detection system usingLVAE, decoders perform processing using the parameters in thecorresponding layers of the encoder in each layer of the decoder.Therefore, by correcting the probability distribution modeled by thedecoder in a data-dependent manner through the encoder, it is possibleto properly perform learning even with a complicated model in which aplurality of sampling operations are performed.

In a fourth embodiment, the case of using auxiliary deep generativemodel (ADGM) as a machine learning model will be explained.

FIG. 10 is a conceptual diagram showing an abnormality detection systemaccording to a fourth embodiment of the present invention using ADGM. InFIG. 10, a solid arrow represents the sampling process, a dashed arrowrepresents copy of data, and a dash-dotted arrow represents calculationof loss L. When ADGM is used for abnormality detection system, learningof the encoder and the decoder is performed as shown in this FIG. 10.However, this ADGM is an extension of the VAE concept of the firstembodiment by adding the auxiliary variable a. In the ADGM, when theinput data x, the latent variable z, and the auxiliary variable a aregiven, when the calculation flow of the arrow in FIG. 10 is expressed byan appropriate neural network, the probability distribution q(z|a, x),q(a|x), z), p(x|z) can all be calculated. It is assumed that p(z) is agiven probability distribution (e.g., standard normal distribution).

The flow of learning processing of ADGM will be described. In thelearning of ADGM, the training data x which is normal data is input intothe encoder, the expression z (latent variable z) of the input data isinferred, the expression z of the input data is input into the decoder,and the restored data x˜ is generated. The feature is the same as thefirst to third embodiments. In this fourth embodiment, further,processing is also performed to infer auxiliary variable a using thetraining data x and the expression z, and also to infer the auxiliaryvariable a from the expression z and restored data x˜. Then, the valueof the loss (error function) L is obtained by the following equation.

L=log [p(x˜|z)]+log [p(a|x˜,z)/q(a|x)]+log [p(z)/q(z|a,x)]

Learning is repeated so that the value of the loss L becomessufficiently small. Since it is difficult to directly calculate the logprobability p(x) in the calculation of the loss L, it is obtained bymaximizing the variational lower limit.

A flow of abnormality detection processing using ADGM will be explained.A learned model with sufficient learning is prepared. The data ofabnormality detection target is input into the encoder of the learnedmodel, the expression of the data of abnormality detection target isinferred, and the restored data is generated from the expression in thedecoder. The obtained restored data is compared with the input data forabnormality detection target, and abnormality is detected from thedeviation between them.

As described above, according to the abnormality detection system usingthe ADGM, the auxiliary variable a is introduced to the processing inthe encoder and the decoder and the processing for inferring theauxiliary variable a is performed at the same time, and therefore, it isexpected that the decoder will be able to model complex probabilitydistributions and the accuracy of generation will be higher.

With regard to a method of abnormality detection, in the firstembodiment, as a method of abnormality detection, it is described thatthe sensor data is determined to be normal or abnormal based onprobability, and the method of this determination can also be adopted inthe second to fourth embodiments. In the first to fourth embodiments,calculation of the probability is not performed, but deviation betweenthe input data x and the restored data x˜ may be calculated so as todetect abnormality or normality according to the amount of deviation.Specifically, the deviation of the component for each dimension of theinput data x and the restored data x˜ is obtained by performingcalculations such as (x_(i)−x_(i)˜)², and if there is large deviation inany dimension, it may be determined to be abnormal.

A first improvement in learning and in abnormality detection is providedas follows. In the first to fourth embodiments, inference of values suchas latent variable z, expression z, auxiliary variable a, and the likeare respectively obtained by sampling from a stochastic function, but ithas been explained that sampling is performed only once, and the latentvariables z, the expression z, the auxiliary variable a, and the likeare obtained to calculate the loss L. However, the present invention isnot limited thereto. It is also possible to perform sampling a pluralityof times, to calculate the loss L for each obtained value, and to obtainthe average. By thus sampling multiple times, deviation in sampling canbe absorbed, so it can be expected to improve learning efficiency and toimprove abnormality detection accuracy.

In a second improvement in learning and in abnormality detection, in thefirst to fourth embodiments, in any of the learning process andabnormality detection process, the input data x is input to the encoder,the expression z (latent variable z) of the input data is inferred, andthe expression z of the input data is input to a decoder to generaterestored data and abnormality detection is performed by comparing theinput data x with the restored data x˜. However, in this case, there isa case where the obtained restored data x˜ is not sufficiently close tothe value of normal data. Therefore, the restored data x˜ obtained byone inference and generation process may be further input to theencoder. For example, the restored data close to the value of normaldata can be obtained by repeating process including generating restoreddata x₀˜ from input data x, generating restored data x₁˜ from restoreddata x₀˜, generating restored data x₂˜ from restored data x₁˜, inputtingthe obtained output to the encoder again. In this case, the loss L maybe calculated for each process of inference and generation, and the sumof the losses L may be calculated, or the restored data finally obtainedby repeating processing a plurality of times (in the example, restoreddata x₂˜) may be compared with the input data x to calculate the loss L.In this way, by calculating the loss L after repeating a plurality ofinferences and generation processes, improvement of learning efficiencyand improvement of abnormality detection accuracy can be expected.

Other embodiments are described as follows. The abnormality detectionsystem 1 can be used for a failure prediction system of a machine and anelectronic device. The failure prediction system according to thepresent embodiment not only predicts event that can occur bysequentially processing data collected from various data sources butalso realizes controlling, with a series of operation, determination ofappropriate action (countermeasure) for the detected event (occurrenceof event) and output processing for performing notificationcorresponding to the action determined for the related system and thepredetermined control.

In addition, for the determined action (occurred event), the actualaction result (including the case where the action itself is notperformed) actually performed by the related system is accumulated asfeedback information, and the detection precision of the event isimproved to make it possible to provide additional information that ishighly usable for the system linked with the supervisory control system.

For example, it is possible to use for a failure prediction system ofmultiple industrial machines and robots in factories, and it is possibleto use for an abnormality prediction system of infrastructure such aselectric power. It is possible to use for an abnormality predictionsystem of multiple parts such as aircraft and automobiles.

The abnormality detection system 1 can be used for prediction system ofreplacement time of consumables and parts. The prediction systemaccording to the present embodiment not only predicts event that canoccur by sequentially processing data collected from various datasources but also realizes controlling, with a series of operation,determination of appropriate action (countermeasure) for the detectedevent (occurrence of event) and output processing for performingnotification corresponding to the action determined for the relatedsystem and the predetermined control.

In addition, for the determined action (occurred event), the actualaction result (including the case where the action itself is notperformed) actually performed by the related system is accumulated asfeedback information, and the detection precision of the event isimproved to make it possible to provide additional information that ishighly usable for the system linked with the supervisory control system.

For example, it is possible to use for prediction and notification ofthe replacement timing of consumables including engine oils of aircraft,automobiles, and the like. It is possible to use for prediction andnotification of the replacement timing of consumables such as drillteeth of a machine tool.

The abnormality detection system 1 can be used for a general purposesupervisory control system. The supervisory control system according tothe present embodiment not only detects event that can occur bysequentially processing data collected from various data sources butalso realizes controlling, with a series of operation, determination ofappropriate action (countermeasure) for the detected event (occurrenceof event) and output processing for performing notificationcorresponding to the action determined for the related system and thepredetermined control.

In addition, for the determined action (occurred event), the actualaction result (including the case where the action itself is notperformed) actually performed by the related system is accumulated asfeedback information, and the detection precision of the event isimproved to make it possible to provide additional information that ishighly usable for the system linked with the supervisory control system.

For example, it can be used for home security monitoring system. It canalso be used for monitoring systems such as buildings, publicfacilities, horticulture and the like.

The abnormality detection system 1 can be used for network securitymonitoring system. The monitoring system according to the presentembodiment realizes controlling, with a series of operation, detectionof an event that can occur by sequentially processing data collectedfrom various data sources, determination of appropriate action(countermeasure) for the detected event (occurrence of event), andoutput processing for performing notification corresponding to theaction determined for the related system and the predetermined control.

In addition, for the determined action (occurred event), the actualaction result (including the case where the action itself is notperformed) actually performed by the related system is accumulated asfeedback information, and the detection precision of the event isimproved to make it possible to provide additional information that ishighly usable for the system linked with the supervisory control system.

The abnormality detection system 1 can be used for medical imagingdiagnostic system. The image diagnosis system according to the presentembodiment realizes controlling, with a series of operation, detectionof an event that can occur by sequentially processing data collectedfrom various data sources, determination of appropriate action(countermeasure) for the detected event (occurrence of event), andoutput processing for performing notification corresponding to theaction determined for the related system and the predetermined control.

In addition, for the determined action (occurred event), the actualaction result (including the case where the action itself is notperformed) actually performed by the related system is accumulated asfeedback information, and the detection precision of the event isimproved to make it possible to provide additional information that ishighly usable for the system linked with the supervisory control system.

For example, CT or NMR image recognition technology is used for earlydetection and early treatment of cancer. In past systems, abnormalityand phenomena were found from these images by doctor's advancedexpertise and judgment of doctors who have extensive experience.However, by using this system, it is possible to detect an abnormalphenomenon (an abnormal tissue image different from a normal tissueimage pattern) with higher accuracy and speed.

The abnormality detection system 1 can be used for quality control ofcell preparations in regenerative medicine. The image diagnosis systemaccording to the present embodiment realizes controlling, with a seriesof operation, detection of an event that can occur by sequentiallyprocessing data collected from various data sources, determination ofappropriate action (countermeasure) for the detected event (occurrenceof event), and output processing for performing notificationcorresponding to the action determined for the related system and thepredetermined control.

In addition, for the determined action (occurred event), the actualaction result (including the case where the action itself is notperformed) actually performed by the related system is accumulated asfeedback information, and the detection precision of the event isimproved to make it possible to provide additional information that ishighly usable for the system linked with the supervisory control system.

For example, when inducing the differentiation of pluripotent stem cellsinto stem cells, progenitor cells or differentiated cells of eachtissue, the heterogeneity of the cell preparation which is the finalproduct due to the nonuniform differentiation efficiency is a problem.Therefore, by using abnormality detection system 1, abnormal cell imagesdifferent from normal cell image patterns can be detected with higheraccuracy and speed.

In the configurations described in each embodiment of the abnormalitydetection system 1 above, the abnormality detection system 1 which ismerely an example can be appropriately changed within a range notdeviating from the technical idea. Further, the configurations describedin the respective embodiments may be used in combination as long as theydo not contradict each other.

As described above, the abnormality detection system 1 can be realizedby one or a plurality of computer devices, and each function can beconfigured as a program. For example, it is stored in the auxiliarystorage device 105 shown in FIG. 2, the control unit such as the CPU 100reads the program for each function of the monitoring control systemstored in the auxiliary storage device 105 to the RAM 101, the controlunit executes the program read to the RAM 101, and the respectivefunctional blocks of the present embodiment can be operated by one or aplurality of computers. That is, one or a plurality of computers inwhich program of each function of the monitoring control system of thepresent embodiment is installed can operate as a computer device(system) performing each function alone or in cooperation.

In addition, the above program is a state recorded in acomputer-readable recording medium, and examples of computer readablerecording media which can be provided to the computer include an opticaldisk such as a CD-ROM, a phase change type optical disk such as aDVD-ROM, magnetooptical disks such as magnet optical (MO) or mini disk(MD), magnetic disks such as floppy (registered trademark) disks andremovable hard disks, memory cards such as compact flash (registeredtrademark), smart media, SD memory cards, memory sticks, and the like.Further, a hardware device such as an integrated circuit (IC chip or thelike) specially designed and constructed for the purpose of the presentinvention is also included as the recording medium.

Although the embodiment of the present invention has been described, theembodiment has been presented as an example, and it is not intended tolimit the scope of the invention. This novel embodiment can beimplemented in various other forms, and various omissions,substitutions, and changes can be made without departing from the gistof the invention. These embodiments and modifications thereof areincluded in the scope and gist of the invention and are included in theinvention described in the claims and the equivalent scope thereof.

As shown in the FIGS, a Reference Signs List is as follows:

-   1 abnormality detection system-   10 storage unit-   11 acquisition unit-   12 measurement unit-   13 determination unit-   14 learning unit

1. An abnormality detection system comprising: a storage device storinga latent variable model and a joint probability model that arepreviously learned; an acquisition unit acquiring input data of anabnormality detection target; an encoder inferring a latent variablefrom the input data based on the latent variable model stored in thestorage device; a decoder generating restored data from the latentvariable based on the joint probability model stored in the storagedevice; and a determination unit determining whether the input data isnormal or abnormal based on a deviation between the input data and therestored data.
 2. The abnormality detection system according to claim 1,wherein the determination unit determines an amount of the deviationbetween the input data and the restored data based on probabilitycalculated according to parameters obtained in processes at the encoderand decoder.
 3. The abnormality detection system according to claim 1,wherein the determination unit calculates a deviation of a component foreach dimension of the input data and the restored data and determinesabnormality when there is a large divergence in any dimension.
 4. Theabnormality detection system according to claim 1, further comprising alearning unit learning the latent variable model and the jointprobability model based on training data composed of normal data.
 5. Theabnormality detection system according to claim 1, further comprising ameasuring circuit constructing the encoder and the decoder by any one ofVAE (Variational Auto Encoder), AAE (Adversarial Auto Encoder), LVAE(Ladder Variational Auto Encoder), and ADGM (Auxiliary Deep GenerativeModel).
 6. An abnormality detection method executed by an abnormalitydetection system including a storage device storing a latent variablemodel and a joint probability model that were previously learned, theabnormality detection method comprising: acquiring input data ofabnormality detection target; inferring a latent variable from the inputdata based on the latent variable model stored in the storage device;generating restored data from the latent variable based on the jointprobability model stored in the storage device; and determining whetherthe input data is normal or abnormal based on a deviation between theinput data and the restored data.
 7. (canceled)
 8. A generation methodfor generating a learned model including a latent variable model and ajoint probability model for performing abnormality detection of inputdata, the generation method comprising: acquiring at least one or morepieces of training data consisting of normal data; inferring a latentvariable from the training data based on the latent variable model;generating restored data from the latent variable based on the jointprobability model; calculating a deviation between the training data andthe restored data; and updating parameters of the latent variable modeland the joint probability model based on the deviation.
 9. Theabnormality detection system according to claim 3, further comprising alearning unit learning the latent variable model and the jointprobability model based on training data composed of normal data. 10.The abnormality detection system according to claim 4, furthercomprising a measuring circuit constructing the encoder and the decoderby any one of VAE, AAE, LVAE, and ADGM.
 11. The abnormality detectionmethod according to claim 6, wherein the determining determines anamount of the deviation between the input data and the restored databased on probability calculated according to parameters obtained inprocesses at the encoder and decoder.
 12. The abnormality detectionmethod according to claim 6, wherein the determining calculates adeviation of a component for each dimension of the input data and therestored data and determines abnormality when there is a largedivergence in any dimension.
 13. The abnormality detection methodaccording to claim 6, further comprising learning the latent variablemodel and the joint probability model based on training data composed ofnormal data.
 14. The abnormality detection method according to claim 6,further comprising constructing an encoder and decoder to respectivelyperform the inferring and generating by any one of VAE (Variational AutoEncoder), AAE (Adversarial Auto Encoder), LVAE (Ladder Variational AutoEncoder), and ADGM (Auxiliary Deep Generative Model).
 15. The generationmethod according to claim 8, wherein the calculating calculates anamount of the deviation between the input data and the restored databased on probability calculated according to parameters obtained inprocesses at the encoder and decoder.
 16. The generation methodaccording to claim 8, wherein the calculating calculates a deviation ofa component for each dimension of the input data and the restored dataand determines abnormality when there is a large divergence in anydimension.
 17. The generation method according to claim 8, furthercomprising learning the latent variable model and the joint probabilitymodel based on training data composed of normal data.
 18. The generationmethod according to claim 8, further comprising constructing an encoderand decoder to respectively perform the inferring and generating stepsby any one of VAE (Variational Auto Encoder), AAE (Adversarial AutoEncoder), LVAE (Ladder Variational Auto Encoder), and ADGM (AuxiliaryDeep Generative Model).
 19. The abnormality detection system accordingto claim 1, wherein the acquisition unit, the encoder, the decoder andthe determination unit are executed by one or more computers.